This invention relates generally to video signal processing and, more particularly, to a CCD camera and a signal processing system for use therewith.
As is known, a CCD (charge coupled device) sensor of the kind currently used in television cameras is a large scale integrated circuit device consisting of several thousand individual wells or pixels which detects an incident light image and develops a television picture signal. Heretofore, the design of such CCD cameras have required a number of compromises. Because of yield problems during manufacture of such sensors, it has been necessary to keep the number of pixels in the LSI chip at a minimum which, in turn, is reflected in the design of the camera system. To take into account the limited number of pixels, two types of cameras have evolved: a first type utilizing three LSI chips in combination with a dichroic prism splitter (for professional cameras), and a second type, primarily for consumer camcorders, utilizing a single LSI chip in combination with a color stripe filter disposed in the optical path of the scene. The latter type sacrifices both resolution and sensitivity in order to get color. If the colored stripes of the filtr are yellow, cyan and magenta the loss of luminance sensitivity is minimized (2/3 of normal) but the signal-to noise ratio of the color signal is worse.
It is known from vision research conducted by applicant and others, reported in the following publications, that human vision cannot perceive changes in high spatial resolution information at as fast a rate as it can perceive changes in low spatial resolution information: "Compatible Transmission of High Definition Television Using Bandwidth Reduction", W. E. Glenn et al., Proceedings of the 37th Annual Conference of National Association of Broadcasters, 1983; "Reduced Bandwidth Requirements for Compatible High Definition Television Transmission", W. E. Glenn et al., Proceedings of the 38th Annual Broadcast Engineering Conference of National Association of Broadcasters, 1984; "Visual Chromaticity-Modulation Transfer Function", Granger, et al., Journal of the Optical Society of America, Vol. 63, No. 9, Sep., 1973. The temporal response of the visual system for the highest spatial frequencies in luminance and for color is about half the speed of that for low spatial frequency luminance. Also, the human visual system has better resolution horizontally and vertically than it does diagonally, which suggests that the number of pixels in a camera can be minimized by using offset sampling; that is, the pixels on adjacent lines should be shifted horizontally by 1/2 pixel. Some chip designers are now using this technique in the CCD imager chips. Another characteristic of the human visual system, which has heretofore been used in most color systems, is that the spatial resolution for color is less than half that of luminance.
It is among the objects of the present invention to utilize these three factors of the human visual system to achieve improved performance of a single chip CCD camera.
A more specific object of the invention is to provide a high performance, real-time, high-resolution CCD color camera.